Dental filling composition of a coefficient of thermal expansion approximating that of natural tooth enamel



United States Patent 3,503,128 DENTAL FILLING "COMPOSITION OF A COEFFI-CIENT 0F THERMAL EXPANSION APPROXI- MATING THAT OF NATURAL TOOTH ENAMELRobert N. Boyd, Maplewood, N.J., and Lawrence Colin,

Previous attempts to achieve such a composition have not beensuccessful. Thus, for example, the employment of fused porcelain,although esthetic, has not proved satisfactory since such material istoo brittle for advantag ous use. Furthermore, previous attempts toimprove the prop- Chappaqua, and Edward G. Kaufman, Lake Success, 5erties of direct filling materials by the incorporation of lI l.tY.,assignlolrs, b nlleslpe assignmerits, tof ll))tintsply various fillers,e.g., silicates in resins, e.g., methacrylate- 11 el'na 7 'p 1011 0 eaware based resins, while improving certain of the deficiencies N0Drawullg- Filed M313 21, 1966, 535,727 of previously employed materials,have not been able to Us. Cl. 32 n1t Cl. A611: 5/02, C08g 51/04 4 Claims10 eliminate the problem of solubility, nor have they been able toehmmate the inherent deficiency of previously employed direct fillingmaterials with respect to incom- ABSTRACT OF THE DISCLOSURE patibilityof the linear coetficients of expansion of the i filling material andtooth.

Process of filllflg a f W Wllhln a @9 Wlth a fil It has now been found,however, that by the employ- Tesln dental filllng Inatenal 0rComposltlon Comprlsmgi ment of the composition of the present inventionwherein (a) from about 5% to about 50% by Weight of a a filler selectedfrom minerals having a negative coeffithetic resin capable of beingcured at a low temperament 9 thermal expanslon, mammals having a verylow ture; and coefficient of thermal expansion, and mixtures of these is(b) a finely divided finer comprising ilamplgyed With a conventional lowtemperature curlng (1 50 to 80% by weight, based on the weight of lqu}ism, cornposmon l a relanvely short the total composition, of one ormore materials settlilg and curmg tlme y i Strength and a having anegative coefficient of thermal expansion; efiicient of thermalexpansion slmilar to that of natural and tooth structure, canberealized.

(2) 0 to by Weight, based on the Weight of 25 It is thereforea principalob ect of the present invention the total composition, of one or morematerials to piovlde a direct dental filhng cqmmsltlon which 18 having alow coefficient of thermal expansion relat1vely free from the1nherentdefic1enc1es of previously employed materials.

The composition is such that the combined coefficient It is a ful'thfirObject f the present i nt n to pr of thermal expansion of the filler andresin closely apduce a low temperature curing direct dental fillingcomproximates that of the tooth enamel over the entire tem- Positionhaving unusual Strength and a y 10w perature range existing within theoral environment. efiiciel'lt f thfifmal e pansio closely appr achingthat Optionally, a silane bonding agent is employed to enhance Of anatural toothadhesion between the filler and resin. It is yet a furtherobject of the present invention to provide a resinous direct dentalfilling material comprisirg a low curing liquid resin and a fillerselected from minerals Th present i ti i di t d t a i l i havinganegative coeflicient of linear expansion, materials forced resincomposition and more particularly to such having 3 W 10W coefficient oflinear expansion, and composition useful as a direct filling compositionfor mixtures Of thesedental purposes. 40 It is still a further object ofthe present invention to Th t commonly l d di t fini materials providesuch a resinous direct dental filling material available to dentiststhat are capable of matching the wherein the filler n resin r b nd byappropriate t th i appearance are th ili t cements d th silanes and suchcomposition additionally contains methacrylate-based resins. Thesesilicate cements and polymerilation Catalysts andacceleratorsmethacr'ylate i h i li it d service as Still further objectsand advantages of the composition dental filling materials for anteriorteeth because of their of the Present invention Will become more pp n frlow strength, excessive solubility in mouth fluids, a d the followingmore detailed description of the invention. their incompatibility withthe tooth structure with respect h h r dense dental filling compositionof the present to the coefficients of linear thermal expansion. Inaddiinvention comprises from about 5% to about 65% by tion. themrthacrylate-based direct :filling materials have W ight of a lowtemperature curing resin, the remainder a relatively high shrinkage uponhardening, and low stiffof said composition comprising a fillercomposition, a mess and low tensile strength. silane bonding agent, andappropriate polymerization cata- The following table is presented tofurther illustrate lysts and accelerators of promoters. variouscharacteristics of these direct filling materials in The resin employedin the composition of the present comparison with natural toothstructure: invention essentially can be any resin material appropri-TABLE 1 Tensile Compressive Indentation Coefficient of Modulus ofstrength, strength, Rockwell expansion Elasticity Material p.s.i. p.s.i.30-y(in.) X1 XlO- (1) Methyl methaerylate 4,0006,000 10, 700 .0o3sa00-1580-100 0.26 (2) Silicate cement 700 23,000-27,000 .0016 7.8 2.1 (3)Enamel 1,500 14,00osa000 .0013 11.4 (is-12.0 (4) Dentin 7,800 50, 0000018 7.8 2. s

For the reasons set forth above, and as illustrated by ate for dentaluse which is capable of producing a hard the above table, it has longbeen the desire of the dental profession to prepare a direct fillingcomposition which possesses high mechanical strength and physicalproperties which closely conform to natural tooth structure andtherefore make it more suitable as a filling material.

In general, the base resin is preferably selected from various polyesterand epoxy resins. Suitable non-limitative materials, for example, arethe propylene glycol fumarate phthalate unsaturated polyesters such assold by the Allied Chemical Co. under the name LS 5275 and by PittsburghPlate Glass (P.P.G.) under the name Selectron 580001; styrene modifiedunsaturated polyesters such as Glidden Glidpol 1008, 6-136 and 4CS50;and epoxy resins, such as sold under the name Ciba Araldite 6020. Also,a newly prepared material, a polymer of Bisphenol A and glycidylmethacrylate, as shown in U.S. Patent 3,194,783 can be advantageouslyemployed in the direct filling composition of the present invention. Itis again noted that the above materials are merely exemplary of thebroad groups that can be advantageously employed in the composition ofthe present invention.

The remainder of the direct dental filling composition of thepresentinvention comprises a filler material, a silane bonding agent, andappropriate polymerization catalysts and promoters or accelerators.

The filler of the dental composition of the present invention compriseseither one or more materials having a negative coefiicient of thermalexpansion, one or more materials having a low coefiicient thermalexpansion, or mixtures of certain of such materials.

Suitable filler materials having a negative coefficient of thermalexpansion include minerals selected from lepoidolite, petalite, betaeucryptite (Li O-Al O -2SiO and spodumene. Of these, beta eucryptite ispreferred.

Those materials having a low coefiicient of thermal expansion that areadvantageously employed in the direct dental filling composition of thepresent invention include, for example, topaz, white beryl, siliconcarbide whiskers and/or fibers, alpha alumina whiskers and/or fibers andzirconium silicate, etc.

Materials from the above two groups can be employed alone, or incombinations of two or more from the same group, or as a combination ofmaterials employing materials having both a negative coefiicient ofthermal expansion and those having a low coefiicient of thermalexpansion.

For the present invention, materials having a low coefficient of thermalexpansion are meant to include those having a coefficient below about15.0 C. Thus, for example, the coeflicient reported for topaz is 4.7 10C., white beryl --l.35 10 C., alumina 8.7x 10 C., and zirconium silicate4.2 lO- C. Of these materials, topaz is preferred. In addition to havinga very low coefiicient of linear thermal expansion, topaz is highlydesirable in that it contains a useful amount of fluoride a cariesdeterrent, and possesses about 30% hydroxy radicals which are extremelyadvantageous in silane bonding.

Of the above materials having a low coeflicient of thermal expansion, inaccordance with this invention, the fibers or whiskers of alumina andsilica carbide are employed primarily as reinforcing agents in thefilled resin dental filling composition. This does not mean, however,that their low coefficient of thermal expansion cannot be convenientlyemployed in producing the desirable properties of the presentcomposition with respect to the coeflicient of expansion.

The minerals having a negative coefficient of thermal expansion whenincorporated in the base resin compensate for the coefiicient of thebase resin such that the reinforced polymerized resin has a very lowcoefiicient of expansion which approaches the coefiicient of expansionof the natural tooth structure.

Although either the minerals having a negative coefficient of linearthermal expansion or the materials having a low coefiicient can be usedseparately in accordance with the present invention, it may beadvantageous to employ materials from both of these groups in the fillercomposition. In this manner, the coefiicient of linear thermal expansionof the filled resin system can be more closely regulated so as toprovide a direct dental filling material having a coefficient closelyapproaching that of the tooth structure.

As a preferred embodiment of the present invention, it has been foundadvantageous to employ, as a major amount of filled resin composition,those minerals having a negative coefiicient of linear thermalexpansion. Such a material is usually employed in an amount of from 50-88% by weight of the total composition or an even greater percentage canbe employed. The remainder of the filler, if any, consists of a minoramount of materials having a low coefficient of thermal expansion alongwith the silane bonding agent.

Although not an essential constituent, the silane bonding agent whenemployed, is usually employed in an amount sufficient to assure adequatebonding of the filler material or materials to the base resin. Usuallyan amount necessary to produce a layer of silane from about one to aboutsixteen monolayers thick on the surface of the filler is advantageouslyutilized in the dental filling composition of the present invention. Ingeneral, such an amount is approximately up to 10.0% by weight of thetotal composition. In addition to bonding the filler to the resin base,the silane bonding agent is also useful in bonding the filled resindental filling composition to the natural tooth. In this manner, thesematerials serve a dual function.

In general, any silane bonding agent that is advantageously employed indental compositions can be effectively employed in the direct fillingmaterial of the present invention. Non-limitative representativematerials include, for example: methacryloxy propyl trimethoxysilane,(N,N) bis-beta-hydroxyethylgamma-amino propyltriethoxy silane,3,4-epoxycyclohexyl-ethyl-trimethoxy silane,glycidyloxy-propyl-trimethoxy silane, vinyl trichlorosilane, tris(Z-methoxy ethoxy) vinyl silane, trimethoxy silyl propyl methacrylate,dimethyl vinyl chlorosilane and various other materials.

Where the base resin is an epoxy resin, those silanes containing anepoxy radical are preferred since greater adhesion is realized from thecombined effect of these materials.

The silane bonding agent is generally added to the filler material, ormaterials, after such reinforcing fillers are heat cleaned at a hightemperature and/or high vacuum in order to remove all absorbedimpurities. Alternatively, howeverfit is possible to add about half ofthe silane to such filler, the remainder being added to the lowtemperature curing liquid resin. In either case, the silane performsboth the functions of bonding filler to resin and assisting the bondingof the filled resin to the natural tooth cavity.

The composition of the present invention can thus be summarized asfollows:

Constituent: Weight percent Resin 565 Silane bonding agent 0-10 FillerRemainder The preferred embodiment of the present invention cansimilarly be summarized as follows:

Constituent: Weight percent Resin 10-40 Silane bonding agent 0.05-8Filler (1)negative coefiicient 50-88 Filler (2)--low coeflicient 0-250.001 to about 5.0% by weight of the total composition. Similarlyconventional promoters or accelerators, e.g. metal acetyl acetonates,cobalt octoate, tertiary amines, etc., are added in an amountcorresponding to about 0.01% to about 3% based on the total dentalcomposition.

The composition of the present invention will be further illustratedwith reference to the following non-limitative examples:

EXAMPLE I The following composition was prepared:

Constituent: Percent by weight P.P.G. Selectron 58001 (a propyleneglycol fumarate phthalate unsaturated polyester) 23.43 Methyl ethylketone peroxide 0.23 Dimethyl aniline in styrene 0.09 12% cobalt octoatesolution in inert vehicle 0.05 Methacryloxy propyl trimethoxysilane 2.12Beta-eucryptite (powdered) 65.65 Topaz (powdered) 8.43

The above composition was found to produce a reinforced resin with acoeflicient of thermal expansion of 19.l27.9 C. over the range of 0 C.to 60 C.;

a setting time of 7 minutes; tensile strength ofv 1600 p.s.i.;

and a compression strength of 8500 p.s.i.

EXAMPLE II The following composition was prepared:

Constituent: Percent by weight Allied Chemical LS 5275 (a propyleneglycol fumarate phthalate unsaturated polyester) 17.45 12 cobalt octoatesolution in inert vehicle 0.02 Aliphatic ketone peroxide I- 0.38Methacryloxy propyl trimethoxy silane 2.15 Beta-eucryptite 80.00

As with the material of Example I, this reinforced resin materialcompared favorably to natural tooth structure with respect tocoefiicient of thermal expansion and tensile strength.

EXAMPLE III The following composition was prepared:

Constituent: Percent by weight Allied Chemical LS 5275 polyester 18.43Quaternary Ammonium chloride promoter 0.10 Aluminum acetyl acetonate0.10 Dodecyl mercaptan 0.19 Aliphatic ketone peroxide 0.38Glycidoxy-propyl-trimethoxy silane 0.80 Beta-eucryptite 80.00

Here again, as in Examples I and II, a reinforced resin which comparedfavorably with natural tooth material was produced. Also, when thealuminum acetyl acetonate accelerator was replaced with cobalt,vanadium, ferrous vanadyl and magnesium acetyl acetonate, similaradvantageous compositions were produced.

EXAMPLE IV The following composition was prepared:

Constituent: Percent by weight P.P.G. Selectron 58001 (polyester resin)19.31 Methyl ethyl ketone peroxide 0.20 12% cobalt octoate solution 0.04Dimethyl aniline in styrene 0.08 Beta eucryptite 78.90 3,4epoxycyclohexyl ethyl trimethoxy silane (2 monolayers) 0.47 Alphaalumina whiskers 1.00

The above composition produced a reinforced resin with a coeflicient oflinear expansion of 2223.9 10- C.

over a range of 0 C.60 C., a setting time of 7 minutes, and a tensilestrength of 2500-2900 p.s.i.

6 EXAMPLE V The following composition was prepared:

Constituent: Percent by weight Glidden Glidpol G-136 (styrene modifiedpolyester resin) 29.16 Benzoyl peroxide 0.71 Styrene 0.57 Zrsio. 68.02

Methacryloxy propyl trimethoxysilane 1.54

The above composition produced a resin with a coefficient of thermalexpansion of 39 10= C., a setting time of 10 minutes, a tensile strengthof 5400-7100 p.s.i., compression strength of 12000, and a hardness of.0025 (Rockwell 30-Y).

EXAMPLE VI The following composition was prepared:

Constituent: Percent by weight Glidden Glidpol G-136 (above) 27.09Benzoyl peroxide 0.68 Styrene 1.35 Methacryloxy propyl trimethoxy silane1.50 ZrSiO 67.88

1 Added to resin with 1.50% of above silane, or powder bydrolyzed byH2O.

In the preparation of this composition, the zirconium silicate wastreated with 1 monolayer of silane calculated according to the area ofthe powder in relation to the area coverage of the silane (approximately3.0%). The coated powder was hydrolyzed in acetic acid and deionizedwater in an ultrasonic vibrator and dried at 230 F.

The above composition produced a reinforced resin with a coefficient ofthermal expansion of 39 10 C., a setting time of 10 minutes, tensilestrength of 5400- 6450 p.s.i., a compression strength of 12,000 p.s.i.,and a Rockwell hardness of .0025.

EXAMPLE VII The following composition was prepared:

Constituent: Percent by weight Ciba Araldite 6020 epoxy resin based onbis-phenol A) 40.0 Boron trifluoride hardener in dibutyl phthalate 20.0

Petalite 36.49

A1 0 whiskers 3.50

Glycidoxy-propyl-trimethoxy silane 0.01

EXAMPLE VIII The following compositions having properties similar tothat of natural tooth materials was prepared:

Constituent: Percent by weight The following composition was prepared:

Constituent: Percent by weight Dow Derakane 1 55.00 Vinyl-estercompound:

Beta-eucryptite 43.00 Benzoyl peroxide 2.06

1 The Dow Derakane resins are thermosetting resins having molecularweights of less than 1,000 and based on bisphenol A. See column 1,Chemical Week, Feb. 26, 1966, page 33.

7 EXAMPLE x The following composition was prepared:

Percent by Weight In most of the above examples the fillers were treatedwith the silane separately and then mixed and added to the resin priorto the addition of accelerators, promoters, :atalysts, or hardeners. Theamount of silane in each case was calculated, based on the area of 100grams of filler and the area of coverage of 1 gram of silane.

As is noted from the above examples, the formulations )f the presentinvention had properties of hardness and itrength and a coefiicient ofthermal expansion similar to hat of tooth enamel and in addition,hardened in less vhan 11 minutes. These properties, therefore, make such:ompositions extremely useful as direct filling materials.

While certain preferred embodiments of the present nvention have beenshown by way of specific example, it s to be understood that theinvention is in no way to as limited thereto, but should be construed asbroadly as lll or any equivalents thereof.

Having adequately described the invention, what is :laimed is:

1. In a process of filling a cavity within a tooth with r. filled-resindental filling composition having a relaively short setting time, theimprovement which com- )rises providing a dental filling having acoefiicient of hermal expansion closely approximating that of naturalooth enamel by using a dental filling composition conisting essentiallyof (a) from about 5% to about 50% by weight of a liquid synthetic resincapable of being cured at low temperatures and selected from unsaturatedpolyesters and epoxy resins; and

(b) a finely divided filler comprising:

(1) 50% to 88% by weight, based on the weight of the total composition,of one or more materials having a negative coefficient of thermalexpansion selected from beta-eucryptite, lapidolite, petalite andspodurnene; and

(2) 0 to 25% by weight, based on the weight of the total composition, ofone or more materials having a low coefiicient of thermal expansionselected from topaz, white beryl, silicon carbide whiskers, siliconcarbide fibers, alpha alumina whiskers, alph alumina fibers andzirconium silicate.

2. The process of claim 1, wherein the finely divided filler is onewhich has been pre-treated with a silane bonding agent in an amount of0.05-8% by weight, based on the weight of the total composition.

3. The process of claim 2, wherein a portion of the silane bonding agentis incorporated in the synthetic resin.

4. The process of claim 1, wherein the filler having a negativecoefiicient of thermal expansion is betaeucryptite.

References Cited UNITED STATES PATENTS 3,194,784 7/1965 Bowen 32-152,035,180 3/1936 Brill 106-35 831,185 9/1906 Rawitzer 106-35 OTHERREFERENCES C. A. Harper: Electronic Packaging With Resins, McGraw-HillBook Co., New York, 1960, pp. 129, 130, 131, 132, 133.

Hummel: Thermal Expansion Properties of Some Synthetic Lithia Minerals;Journal of The American Ceramic Society, 1951; vol. 34, pp. 235-239.

MORRIS LIEBMAN, Primary Examiner L. T. JACOBS, Assistant Examiner U.S.Cl. X.R.

